The following article was written by Dan Pike, group executive, Filter Manufacturers Council (FMC) and vice president, membership and members services, Automotive Aftermarket Suppliers Association.
It’s time to clear the air about filters — those automotive components which keep your customers’ vehicles running clean.
Here is a brief overview of motor vehicle filtration products, which include filters for the engine, oil, cabin air and transmission.
Filters: It’s what’s inside that counts
Any discussion of motor vehicle filters begins with filter media — the material inside the filter which captures dirt and foreign particles.
Filter manufacturers use many different types of media for various fluids and environmental extremes. The most common used filter media are cellulose-based and glass.
Cellulose media is manufactured with fibers of various sizes. On the top layer of the media, the fibers are fluffed up, rather than compacted down. When fluid and contaminants pass through the media, many particles collect on the fluffy fibers on the surface and don’t travel further into the filter.
Glass media was developed to be utilized in hydraulic systems because it has low flow restriction at high filtration efficiencies. These low-flow resistance properties are beneficial in hydraulics where cold oil is being forced through the media and when filtration in the 3 to 5 micron range is desired.
Glass media has a drawback regarding capacity. Typically, glass media has the same pore size and same fiber diameter through the entire sheet. The media can be manufactured to be very efficient, but then it is so tight that it has very little life or capacity.
Synthetic media is making inroads in replacement filters. In most lube, fuel and air filter applications, cellulose media remains the better choice. As with glass, the reason largely relates to capacity, or filter life. A brief description of the filtering process illustrates this.
The process of fluids and contaminants collecting on the fluffy fibers of cellulose filter’s surface is called “adsorption.” The particles adhere to the surface fibers and don’t travel farther into the filter.
The more adsorption a media applies, the more small particles can be separated before they reach the small pore spaces on the screen side of the media. This keeps these small particles from plugging the media.
Cellulose media typically is thicker than synthetic. The thicker the media is, the more time the particles spend traveling through it. Each time the fluid changes direction around a fiber, the momentum keeps particles traveling in the same direction they were going and they are driven into the fibers.
This particle separation is called “impingement.” As with adsorption, the more impingement that a media applies, the more particles are separated without plugging the tight pore space on the screen side.
Synthetic media does separate some particles with adsorption and impingement, but the smooth fibers can’t hold the particles in place. Often they are washed off with the fluid traveling through the media.
Synthetic media primarily uses the particle separation technique called “direct interception.” Direct interception is simply separating particles by passing the fluid through pore spaces that are small enough to catch them. However, once all pores are filled with the contaminant, the filter is plugged and its life is over.
Because cellulose media is better at adsorption and impingement, it can remove more contaminants than glass or synthetic media without plugging pore spaces.
Can a synthetic media be created with the benefits of cellulose media? This remains to be seen. For now, both cellulose-based media and glass media have a place in today’s filter market.
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